The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Combustion within an engine involves introducing fuel and air into a combustion chamber. Timing of the events involved in combustion and the properties of the resulting combustion affect the resulting efficiency and emissions of the engine. In diesel engines, chemical properties of diesel fuel can affect auto-ignition timing and therefore affect engine efficiency and emissions.
Diesel fuels are designated with a cetane number which indicates the ability of the diesel fuel to auto-ignite when injected into compressed air in a combustion chamber of a diesel engine. Cetane numbers affect a progression and an intensity of the resulting combustion. The higher the cetane number of the fuel, the more quickly auto-ignition occurs following an injection. Diesel fuels with lower cetane numbers have a greater ignition delay and thus slower auto-ignition. Similarly, given a fixed mass of fuel, the higher the cetane number of the fuel in a combustion event, the greater the magnitude of the energy release in the resulting combustion will be. Commercially available diesel fuels commonly have cetane numbers in a range of 40 to 55. Diesel fuel cetane numbers may vary each vehicle fill up, thereby varying an average cetane number of the diesel fuel stored in the vehicle fuel tank.
Pressure sensors in the combustion chambers have been used to determine combustion timing and phasing. Known methods for evaluating magnitude measured as signal power or for evaluating combustion phasing rely on estimating heat of combustion, the work performed by combustion, or other reactive metrics. These methods review historical data and react to trends or accumulated data points in the combustion data.
Diesel engines operating under compression ignition are sensitive to changes in fuel properties, as small variations in cylinder conditions can interfere with conditions necessary to create ignition at a desired point in the combustion cycle. Some diesel engines are known to utilize pre-mixed charge compression ignition (PCCI) combustion, wherein the charge is brought to a condition creating auto-ignition of substantially the entire charge at once, allowing improvements in efficiency, fuel economy, and low emissions. Changes in fuel properties affect auto-ignition utilized in PCCI and the properties of the resulting combustion, thereby affecting the benefits of efficiency, fuel economy, and low emissions. Similarly, it will be appreciated that low temperature combustion in a diesel engine is dependent upon properties of the fuel and the resulting combustion.
Compression-ignition engines and other engine control schemes operate over broad engine conditions. Fuel control, fuel tailoring, charge ignition timing control, and exhaust gas recirculation (EGR) control are used to meet operator demands for performance and fuel economy and comply with emissions requirements. Variability in combustion affects heat release and work output from individual cylinders, resulting in undesired performance of the engine.